Process of producing tin tetrachlorid.



P. WOLFE. PROCESS OF PRODUCING TIN TETRAOHLORID. APPLICATION FILED AUG. 17, 1909.

1,087,522. Patented Feb.17,1914.

nvmwrw; l 1

rrnn srawnnr crates.

PAUL WOLFE, OF WETZLAR, GERMANY, ASSIGNOR, BY MESITE ASSIGNMENTS, TO VULCAN DETINNING COMPANY, A CORPORATION OF NEW JERSEY.

PROCESS OF PRODUCING TIN TETRACHLORID.

Specification of Letters Patent.

Fatented Feb. 1?, 31%14.

Application filed August 17, was. Serial no. 513,353.

of philosophy, chemist, and a subject of the- German Emperor, and resident of Kaiserstrasse 8, Wetzlar, 1n the Empire of Germany, have invented new and useful Improvements in Processes of Producing Tin Tetrachlorid, of which the following is a specification.

It being known that tin combines with chlorin to form tetrachlorid of tin, it is obvious that theoretically it is the same whether the tin is in the form of blocks or exists in materials containing tin or the tin coating of tin plate. But all attempts to manufacture commercially tetrachlorid of tin by the simple action of undiluted chlorin have not been practically successful. The chlorin combined not only with tin but, for example, also with iron, whether the iron of the tanks in which the chlorin was made to act or the iron of the tin plate clippings which constituted the principal raw material. The generally accepted explanation of this attack on the iron, viz., that it is due to the heat evolved in the conversion of tin into tetrachlorid, is only correct with considerable limitations. Yet it was generally accepted, because, as the Vessels in which the reaction was effected were closed and opaque it was diflicult to observe closely the phases of the reaction, and consequently, to discover the source-of prejudicial secondary reactions, for it must be remembered that an experiment made on a small scale in a laboratory is different from a manufacturing process. Since the heat of combination was considered to be the only cause of the aforesaid secondary reactions, the temperature produced by this heat was diminished by diluting the chlorin with air. The more air the chlorin contains, the slower becomes the reaction. The tin is consumed more slowly and the same amount. of heat is developed within a longer time. Even in the most recent methods of stripping tin by means of chlorin, chlorin diluted with air is prescribed.

The present method differs from those that are known chiefly -in that undiluted chlorin is used.

' I have found that. it is easy to regulate the temperature of the reaction by diminishing the rate at which the undiluted chlorin is supplied, the efiect being the same as that produced by diluting the chlorin with an indifi'erent gas, as has been the practice hltherto. I have found that it is permissible to allow the temperature of the reaction to rise to, 100 C.; for at this temperature pure chlorin does not attack iron; when mixed with stannic chlorid, it does not attack iron even at a much higher temperature. The time which should be occupied by the chlorination may be calculated, and as an example the following data will be assumed: The reaction tank is of 2 meters diameter and 5 meters deep with a surface of 38 square meters, and weighs 6 tons; there are 14 tons of material containing 2.35 per cent. of tin, making the weight of tin 330 kilos. This quantity of tin develops 330 1o78=355740 calories when converted into tetrachlorid. The total amount of iron in the tank is 20 tons. If the atmospheric temperature is 20 (1., this 1r0n may become heated 80 (1., for which are required, the specific heat of iron being 0.1138,

80 20000 0l138=182080 calories.

So that there remain:

355740182080=173660 calories.

The coeflicient of heat permeability of iron being 8, 38 square meters of tank surface Wlll radiate per hour '38 80 8:24t320 calories.

Thus the 173660 calories to beradiated Will be dissipated in a little over 7 hours. But under the conditions known at present it is very difficult to regulate the supply of chlorin for 7 hours in such a manner that the quantity of chlorin necessary for the Whole reaction is consumed uniformly so as to keep the temperature of reaction as constantly as possible at 100 C. For, when chlorin enters a tank filled with dry goods,

the stannic chlorin is partly evaporated into the air contained in the tank, so that thick clouds of stannic chlorid are formed. When the temperature rises, these, together with the air and the chlorin expand and ,thus ,in.--

crease considerably th ressure inthe tank. This circumstance, which is quite beyond,

iio

human control,- rendered it necessary in former processes to supply the mixture of air and chlorin under pressure, as by a pump or by heating it so that the pressure of the reagent supplied to the tank is higher than the natural reaction pressure. As this latter varies continuously, it is inevitable, that the supply and the consumption of the reagent should become irregular.

The process proceeds better if the air is expelled from the tank and undiluted dry chlorin is used. It does not matter how the air is expelled. As chlorin is heavier than air and mixes with it only slowly, the air can be simply and rapidly expelled by supplying chlorin to the lower part of the tank under as low a pressure as possible and at the same time drawing the air from the upper part of the tank. As soon as the green color of the chlorin becomes visible through a window in the upper part of the tank, the latter is closed, or the supply of clorin is interrupted.

The known reaction begins after a short time, but no vapor of stannic chlorid is produced because in absence of air the chlorid assumes a liquid condition. F or this reason, its volume is small, and in spite of increased temperature there is no pressure; on the contrary, it has been found that the vacuum meter, which had been at 0 (corresponding with a mercury column of 760 millimeters) moved backward to about minus 250 millimeters. The reduced pressure thus created suflices to introduce chlorin into the tank, and it is easy so to regulate the supply during the whole process, that the temperature and pressure remain practically constant, and no more chlorin is drawn in than is steadily consumed without affecting the temperature of reaction. The air can of course also be removed by suction prior to the admission of the chlorin. After the vacuum has been created the process is the following: Undiluted chlorin passes into the evacuated chamber, so that, before the chlorin begins to unite with the tin, this vacuum is partly destroyed and the vacuum meter very soon'shows 100 to 250 mm. in

its mercury column. When the reaction begins, a simple turning of the chlorin cock serves to regulate the current of chlorin, so that the above mentioned pressure may remain permanently constant, as desired Such a simple and easy regulation of the chlorin supply has not hitherto been possible. As the chlorin is mixed with no other gas which could remain unused in the container, any increase over the desired pressure is impossible. In other words, the chlorination takes place practically under constant pressure. chlorin, although mixed with no other gas, is constantly in an attenuat d condition, and the greater the vacuum, the more attenuated At the same time the will be the chlorin and the slower the reac tion. By regulating the degree of the vacuum as desired, a means has been found for retarding the course of reaction it and as the same may become necessary. As soon as the temperature falls, and the pressure rises, the process is completed. It is to be noted that this increase in pressure takes place only after the detinning process has been completed and is a phenomenon not connected with the chlorination process.

A specific form of apparatus for carrying out the process is shown in thedrawing.

a is a reaction vessel provided with a cover 6, and a steam jacket 0. The steam passes in through the pipe (Z and out through the pipe 0; f is the still head; 9 is a cooling coil placed inside of the cooler h; i is the vessel for receiving the product of distillation, which is provided with a suction pipe 70, Z is the thermometer which extends into the vessel from above; m are iron baskets of which a greater or less number is placed in the vessel. These baskets receive the packets of scrap p which are to be detinned and are provided with apertures n so as to permit the chlorin to enter as freely as possible. The baskets are provided with chains 0 for lowering them into and raising them out of the vessel by crane or other means. 9 is the inlet pipe for chlorin gas; 1" an observation glass for the purpose of observing whether the vessel contains chlorin,-s a manometer and t a suction pipe.

When I remove the air from the vessel a by suction prior to the introduction of the chlorin gas, I'may dispense with the observation glass 7' and the suction pipe 2?.

Hitherto, the removal of the tetrachlorid of tin from the goods has proved very diflicult. So far as the liquid product is concerned the removal is easy, for this portion collects at the bottom of the tank and may be tapped and distilled as a separate process. For removing the considerable quantities remaining in the goods, Goldschmidt proposed to evacuate the tank and fill it with hot, dry air; this air having mixed with the vapors was to be drawn off by a pump. Experience has shown that this is very slow. It requires much more time than the process itself. Moreover, considerable quantities of air are necessary and the air must not only be heated but also dried by sulfuric acid or chlorid of calcium. All this is very expensive.

I have found a mode of distilling not on the portion of the tetrachlorid attached to the goods, but the total product in such a manner that the distillate can, without further preparation, be used for weighting silk. This appears impossible at first sight, todistil the product through the whole charge of entangled and compressed tin plate clip pings. A simple distillation is impracticable, because in order to overcome the total sure which may exist in the tank, the chlorid of tin passes over completely and in a remarkably short time. The product thus obtained is tetrachlorid of tin, clear asjwater and free from chlorin, iron or like impurity,

being a marketable product almost chemlcally pure.

It is very easy to heat the tank to the boiling point of tetraohlorid of tin because its contents are, or may be, already at 100 C. owing to the heat of reaction. As'tet-rachlorid of tin boils at 11430., an increase in temperature of only 14 C. would be nec essary. According to the degree of diminution of the pressure however, tin tetrachlorid boils at 100 C. and even at temperatures below that. I have found that at 360 mm.

. mercury the tetrachlorid boils at 100 C.

Since, as already stated, it is possible to maintain such a low pressure during the process when undiluted chlorin is used it is possible to distil intermittently even before the process is finished, as soon as the temperature has risen to 100 C. and a sufficient quantity of tetrachlorid has formed. From this it follows that the advantage of employing undiluted chlorin in themanner specified is not limited to diminishing the rate of the reaction, which might also be obtained by other means. The chlorin withdrawn from theprocess by this distillation may be returned to the process or may be condensed in a known manner in suitable aqueous solutions together with any vapor oftetrachlorid carried by the chlorin. Such carried vapor is, however very small in quantity owing to the low vapor tension of the tetrachlorid of tin. i V

A further advantage of the distillation under diminished pressure isits applicability for purifying tetrachlorid of tin containing chlorin. In all known methods .a

more or' less considerable excessof chlorin in the tetrachlorid of tin is scarcely to be avoided. A simple re-distillation does not suffice to remove the excess of chlorin,lbecause theychlorin is always carried over again. In the distillation under diminished pressure, on the contrary, the chlorin is con tinuously removed.

It is obvious that distillation under 'diminished pressure may also be employed for winning tetrachlorid of tin by means of chlorin from materials containing tin other than tin plate clippings. Here also the re sult will be that pure tetrachlorid of tin is obtained.

It is, of course, essential that not only must the process be conducted under perfectly dry conditions but that the goods.

used must be sufliciently dry.

The characteristics of the process are the facts: (1) that undiluted chlorin is used, air being excluded or expelled; (2) that tetrachlorid of tin is obtained as a marketable product directly from the tank by distillation' under diminished pressure.

Now what I claim and desire to secure by Letters Patent isthe following:

1. In the process of obtaining tetraohlorid of tin, the improvement which consists in placing a body of dry tin-bearing material in a vessel, filling said vessel with substantially pure chlorin as rapidly as possible until the tin-bearing material is completely immersed in the chlorin gas and the air displaced closing the vessel against the admission oii air as soon as it is filled with chlorin, permitting the reaction between chlorin and tin to proceed while the body of the chlorin is in a quiet, una'git-ated condition until the pressure in the vessel is materially reduced, and maintaining the said reduced pressure thus created while continuing to admit limited quantities of chlorin gas until det-inning is completed.

2. In theprocess of obtaining tetrachlorid of tin, the improvement which consists in immersing dry tin-bearing material in a quiet unagitated mass of substantially pure chlorin, the said chlorincompletely enveloping the entire mass of tin-bearing material, but not being-of suflicient pressure to cause the entire mass of tin to be converted into tetrachlorid, and regulating the further admission of chlorin to the vessel so that the reactions in the vessel of themselves maintain the contents of the vessel at reduced pressure. Q

In testimony, that I claim the foregoing as my invention, I have signed my name in presence of two witnesses.

DR. PAUL WOLFE. Witnesses:

HANS VON SoHU'rz, 

